Regioselectivity and kinetics of fluorination of alkyl substituted phenols by N-fluoro-1,4-diazoniabicyclo[2.2.2]octane salt analogues

The 3,4-dialkylsubstituted phenols: 3,4-dimethylphenol, 5-indanol, and 5,6,7,8-tetrahydro-2naphthol were used as target molecules for fluorination with the N-fluoro-1,4diazoniabicyclo[2.2.2]octane salt analogues Selectfluor TM F-TEDA and Accufluor TM NFTh.4-Fluoro-3,4-dialkylcyclohexa-2,5-dienone derivatives, as the result of an addition-elimination process, were the main, and 2-fluoro-and 6-fluoro-3,4-dialkylphenols derivatives resulting from a substitution reaction, the minor products of the fluorination process.The type of transformation was found to be independent of the structure of starting material and reagent, while these two parameters were important for the regioselectivity of the substitution reaction.The effect of the solvent on these reactions was evaluated, second order kinetics for the fluorination with F-TEDA in MeCN was established, rate konstants k 2 were measured, and thermodynamic parameters for the transition state (∆H * , ∆S * , and ∆G * ) determined.A reaction pathway postulating a SET process as the key step was proposed.

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